The field of the invention relates to float valves for use in running casing into wellbores or running other downhole tools into a wellbore with close clearances at higher speeds.
Rig time is costly to well owners and operators. One way to cut down on rig time is to be able to increase the rate at which casing is run into a wellbore. Casing normally includes a check valve near its lower end. This valve can be locked open during running to allow fluid entry inside of the casing. This check valve contains a fairly small open area in the order of approximately 3 square inches when casing in the order of 9⅝ to 13xe2x85x9c inches in diameter is being run. The small opening size in this check valve limits the rate of advancement of the casing into the wellbore. An overly aggressive advancement rate results in undesirable fluid pressure buildup on the formation adversely affecting well control and future productivity of the formation.
Another typical choke point apart from the check valve at the bottom of a casing string is through the wiper plug near the top of the casing when it is being run in. Typically the cross sectional area in the flow bore through the wiper plug assembly is in the order of about 3 square inches.
Accordingly, it is an object of the present invention to optimize the available open area during run in to allow higher running rates for the casing. The apparatus of the present invention is useful not only in running casing but can also be useful in running downhole tools in wellbores with fairly low clearances.
A check valve assembly for the bottom of a casing string with increased open area is provided. Multiple check valves are provided are provided for assurance of ultimate closure. Bypass flow paths in the area of the check valve and the wiper plug are available during run in that increase the normal available open area from about 3 square inches to a range of about 10 square inches and even higher. Components freely float during run in to provide the greater open area and are subsequently repositioned with known techniques of dropping a ball and pressurization when the casing has reached the desired depth.